They did it for a number of reasons, but the primary one we heard about? They did not want to have to start designing non-raid content that required raid gear.
Think about it this way: A sizable chunk of the playerbase gets radiance gear, at least three or four pieces. They start running around with not just an eternal hope buff that messes with the dread mechanics, but also increases their morale, their healing, their damage done and reduces damage taken.
It makes older content trivial, but what is worse, it starts making on-level (LOTRO Gold) content trivial. Because if the content is designed to be at least moderately challenging for people WITHOUT radiance gear, just imagine what it is to people that are hopped up on hope.
So instances have to start being designed with the assumption that people already have the gear. But how much? Where the bar should be put? And what is more, if content starts being designed across the board with rad-buffed players in mind, where do players with NO radiance fall? The entire game post-Moria would be gated by the Moria instances.
Hope something in the message above helped! If you want to get a Lord Of The Rings Gold for your character, or want to buy cheaper Gold for your character in the game. Our site is your best choice. Hope you enjoy yourself in this wonder game.